Rear suspension systems are known which include a circular section rubber torque spring developed by B. F. Goodrich. This type of torsion spring includes a molded, cylindrical, tubular shaped, vulcanized rubber body having an inner cylindrical steel pipe and a steel sheet outer casing substantially as shown in FIGS. 1A and 1B. The spring is represented in FIG. 1A in the disassembled and in the assembled condition in FIG. 1B. FIG. 2 illustrates an end view of the conventional torsion spring assembled on the rear of a vehicle.
The conventional rubber torsion spring assembly 1 shown in FIG. 1A comprises a vulcanized rubber torsion body 2 pressure inserted inside a thin-wall pipe 3. The pipe 3 includes a pair of strong steel shells 4 firmly welded to the pipe 3 to form a support structure for the rear axle. A steel tubular pipe or shaft 5 extends through the rubber body 2 and extends from each end of the rubber body 2. As shown in FIG. 1, the rubber body 2 typically includes a steel sleeve fixed to the rubber body before inserting into the pipe 3.
For the suspension assembly 1 to support the load of the bus, the spring assembly 1 must be tensioned as known in the art. Adjustment levers 6 may be welded on the ends of the steel tubular shaft 5. To form the complete rear suspension for a vehicle, two spring assemblies 1 are required, as described above, which are firmly fixed to opposite ends of the rear axle of the vehicle via U-shaped bolts and base plates. The rear axle is rigid and incorporates the differential assembly by means of which the bus is driven.
To complement the suspension assembly 1 and allow relative movement of the axle with respect to the body, the suspension has a pair of arms 7 articulated on each end of the tubular shaft 5 as shown in FIG. 2. An adjustment block 8 sustains the arm 7 via the threaded tension member 9 and positions the arm 7 relative to the vehicle whereby the height of the vehicle body is adjusted in relation to the ground when the spring undergoes normal relaxation due to use.
The suspension assembly 1 also incorporates four couplings 10, each comprising a rubber lined steel core and a casing. Each coupling 10 is joined to the arm 7 and the support 11 of the vehicle body. The rubber lined steel core of the coupling 10 isolates the vibration of the tires and also allows pivotal movement to permit movement of the axle in relation to the body, or of the body in relation to the axle, as in conventional suspension systems.
Although the above-described assembly of circular section rubber torque springs satisfactorily meets the fundamental safety and comfort requirements for proper operation of the bus, this system has the inconvenience that once the tension member 9 thread is used up, which allows adjustment of the springs, the adjustment levers 6 of the springs have to be removed from the steel shaft 5 and welded again in another angular position on the ends of the tubular steel shaft 5 to compensate for the permanent, progressive deformation of the rubber body that occurs with use. The process of welding the adjustment levers 6 to the tubular shaft 5 results in application of heat, thereby damaging the rubber body near the end of the shaft causing a reduction in its use life.
Another inconvenience of the conventional rear suspension assembly is the excessive time required in replacing the spring assembly when they must be removed at the end of their useful life. The replacement operation of these spring assemblies requires the use of a press to pull or push the rubber torsion spring inside the steel core and require the availability of a machine shop.